The invention relates to the field of signal transmissions, especially within the super-high frequency (SHF) range. More particularly, the invention relates to a dielectric resonator oscillator for transposing audio signals into the SHF frequency range. The invention also relates to a voice control device.
SHF dielectric resonator oscillators (DROs) are commonly used in devices for transmitting SHF signals, enabling high-performance oscillators of small size and of low cost to be obtained. They are especially used as a local oscillator for frequency transposition in low-noise converters for satellite reception.
FIG. 1 shows schematically a dielectric resonator oscillator 1 with a tuning screw, of the prior art. The latter comprises an electromagnetic cavity 2 delimiting by its walls 3 a dielectric resonator 4 coupled to a first microstrip line 5. A circuit 7, illustrated in FIG. 2 showing another resonator of the prior art, the rest of which will be described below, is common to the two resonators and fulfills the same functions. Consequently, the description of the main components of this circuit 7 will be made with reference to FIG. 2. In general, in order to simplify the description, the same references will be used to denote the elements fulfilling identical functions in the present application. The coupling line 5 is, on the one hand, connected to the active circuit 7 and, on the other hand, to an impedance matching load 6. The active circuit 7 comprises an active element 8, of the bipolar transistor or FET type, an element 9 destabilizing the active part, for example of the LC circuit type, and an output impedance matching element 10, of the microstrip line type. It is known that the RLC circuit equivalent to the resonator is the source of damped oscillations, the damping of these oscillations being due to the resistive part of the RLC circuit. This active circuit with a negative resistance then has the function of providing the energy needed to maintain the oscillations, so that the signal delivered to an output 12 of the oscillator is an undamped oscillating signal. It is also known to a person skilled in the art that the assembly formed by the resonator coupled by the microstrip line to the active circuit must exhibit oscillation conditions favorable to the oscillation frequency sought. In the oscillator of FIG. 1, a screw 13 enters the wall 3 of the cavity opposite the dielectric resonator 4. Its degree of penetration in a direction perpendicular to the surface opposite the resonator generates a disturbance in the distribution of the electromagnetic fields in the cavity and, subsequently, a modification of the resonant frequency of the equivalent resonant circuit. Thus, varying the distance d between the end part of the screw entering the cavity and the upper surface of the resonator involves modifying of the frequency of the signal generated by the oscillator. However, this type of oscillator, involving manual adjustment of the distance d, does not allow the fine variations around a central frequency to be faithfully complied with, and without distortion; it is therefore not suitable for transmitting audio signals.
In order to overcome problems linked to the mechanical adjustments as mentioned above, oscillators called electronic oscillators are also known, as illustrated in FIG. 2 showing a dielectric resonator oscillator with a varactor. A varactor 11, connected to a second microstrip line 17 coupled to the dielectric resonator, receives a control signal Sc of variable voltage indicating an audio signal to be transmitted. The resonator-varactor assembly behaves like a resonant circuit setting the oscillation frequency of the oscillator. Thus, the variation in the voltage delivered by the signal Sc modifies the oscillation frequency of the oscillating circuit 7. However, the use of a varactor has the effect of degrading the phase noise of the oscillator and consequently of degrading the quality of the signal generated at the output of the oscillator.
The object of the invention is to overcome the problems of the prior art by providing a dielectric resonator oscillator for transposing audio signals.
To this end, the invention is a dielectric resonator oscillator, comprising a dielectric resonator contained in a resonant cavity in order to generate a signal oscillating at a predetermined central frequency, the dimensions of the resonator and the limiting conditions in the cavity being capable of determining the resonant frequency of the resonator. A means sensitive to acoustic pressure waves is capable of modifying the distribution of the electromagnetic fields in the cavity as a function of said acoustic pressure waves. The means sensitive to acoustic waves comprise a membrane which is movable under the effect of acoustic waves, said membrane engaging a metal coil in the cavity.
Thus, the means sensitive to acoustic pressure waves directly change in time with the acoustic pressure exerted at one of the inputs of said sensitive means. In this way, the invention makes it possible to generate a signal modulated directly by the audio signal at this input.
According to one embodiment, said means sensitive to acoustic pressure waves comprise acoustic transducer means for converting the acoustic pressure waves into a displacement of at least part of detachable means facing the resonator, the displacement of at least part of these detachable means under the effect of acoustic pressure waves being capable of modifying the distribution of the electromagnetic fields in the cavity.
According to one embodiment, the displacement of said detachable means is carried out in the form of vibrations.
According to one embodiment, the means sensitive to acoustic waves comprise a membrane which is movable under the effect of acoustic waves and can engage a metal coil in the cavity.
According to one embodiment, the oscillator comprises adjustment means to adjust the central frequency of the resonator.
According to one embodiment, said adjustment means comprise an adjustment screw which can be engaged in the cavity in order to modify the distribution of the electromagnetic fields therein.
According to one embodiment, the oscillator comprises switching means to switch the modulation by acoustic waves of the signal generated by the resonator to modulation by data transmitted over a channel.
According to one embodiment, an active dipole is coupled to said resonator by coupling means in order to maintain the oscillations.
The subject of the invention is also a voice control device, characterized in that it comprises an oscillator according to the invention.